The present invention relates to a liquid crystal projector using a transmission liquid crystal panel, or more in particular to (1) a liquid crystal projector for projecting the illumination light from a light source on a liquid crystal panel, and projecting an image of the liquid crystal panel on a screen through a projection lens. The invention also relates to (2) a liquid crystal projector in which the illumination light from a light source is split into three colors of R, G and B by a dichroic mirror and irradiated on three liquid crystal panels, images on the three liquid crystal panels are synthesized in color through a dichroic prism and a synthesized image is projected on a screen through a projection lens. Further, the invention relates to (3) a liquid crystal projector in which the illumination light from a light source is irradiated on a liquid crystal panel through a reflector, a first lens array and a second lens array so that the light emitted from the liquid crystal panel is projected on a screen by a projection lens.
A conventional liquid crystal projector using a transmission liquid crystal of this type is known, as described in JP-A-63-216026, for example, which comprises a light source (corresponding to 21), a first reflection mirror (corresponding to 23), a first dichroic mirror (corresponding to 26), a second reflection mirror (corresponding to 30), a second dichroic mirror (corresponding to 27), a third reflection mirror (corresponding to 28), a fourth reflection mirror (corresponding to 29), a first transmission liquid crystal panel (corresponding to 33), a second transmission liquid crystal panel (corresponding to 39), a third transmission liquid crystal panel (corresponding to 45), a dichroic prism (corresponding to 49) and a projection lens (corresponding to 50), wherein the illumination light from the light source is irradiated on the first dichroic mirror through the first reflection mirror, the first emitted light split in color by the first dichroic mirror is irradiated on the first liquid crystal panel through the second reflection mirror, the second emitted light split in color by the first dichroic mirror is irradiated on the second dichroic mirror, the first emitted light split in color by the second dichroic mirror is irradiated on the second liquid crystal panel, the second emitted light split in color by the second dichroic mirror is irradiated on the third liquid crystal panel through the third reflection mirror and the fourth reflection mirror, the transmitted light from the first liquid crystal panel, the transmitted light from the second liquid crystal panel and the transmitted light from the third liquid crystal panel are synthesized in color by the dichroic prism, and the emitted light thus synthesized in color is projected on the screen by the projection lens.
Another conventional liquid crystal projector is known, as disclosed in JP-A-3-10218, comprising an exhaust fan (corresponding to 15, 27) for cooling a light source.
As disclosed in "High-Efficiency Illumination Optical System for Liquid Crystal Projector Using Deformed Open Lens Array", 22Fa06 of Optical Federation Symposium, Hamamatsu '94, pp.135-136, JAPAN OPTICS '94, sponsored by the Japan Optical Society (Application Physics Association), for example, a liquid crystal projector is known, comprising a light source including a metal halide lamp and a parabolic mirror, a UV-IR cut filter, a first lens array and a second lens array.
A liquid crystal projector configured of a combination of the above-mentioned three conventional liquid crystal projectors already finds applications. The prior art will be described below with reference to the drawings.
FIG. 9 is a diagram showing an optical system of a liquid crystal projector comprising a combination of the above-mentioned configurations of the conventional liquid crystal projectors.
The illumination light 51 from a metal halide lamp 50 constituting a light source enters a lamp reflector 52 of a parabolic mirror, a UV-IR cut filter 53, a first lens array 54, a cold mirror 55 constituting a first reflection mirror, a second lens array 56, and a first dichroic mirror 57 for transmitting the R color light and reflecting the G and B color light, so that the R color light 58 is transmitted and the G and R color light 59 are reflected. The R color light 58 is reflected on an increased reflection aluminum mirror 60 constituting a second reflection mirror, and enters a R color light liquid crystal panel 63 constituting a first transmission liquid crystal panel through a condenser lens 61 and a polarizing plate 62. The G and B color light 59 enter a second dichroic mirror 64 which reflects the G color light and transmits the B color light, so that the G color light 65 is reflected and the B color light 66 is transmitted. The G color light 65 enters a G color light liquid crystal panel 69 making up a second transmission liquid crystal panel through a condenser lens 67 and a polarizing plate 68. The B color light 66, on the other hand, enters a B color light liquid crystal panel 76 making up a third transmission liquid crystal panel through a relay lens 70, an increased reflection aluminum mirror 71 making up a third reflection mirror, a relay lens 72, an increased reflection aluminum mirror 73 making up a fourth reflection mirror, a condenser lens 74 and a polarizing plate 75.
The R transmitted light 77 from the liquid crystal panel 63, the G transmitted light 78 from the liquid crystal panel 69 and the B transmitted light 79 from the liquid crystal panel 76 are synthesized in color by a dichroic prism 80. The emitted light 81 thus synthesized in color is projected on a screen (not shown) by a projection lens 82.
In order to prevent the heat generated by the high-temperature light source from having an effect on the component parts other than the light source, an exhaust fan 83 for cooling the light source is arranged in the neighborhood of the metal halide lamp 50 and the lamp reflector 52 thereby to exhaust the hot air 84 out of the housing (not shown) of the liquid crystal projector.
The liquid crystal projector having this configuration can produce a bright, large image on the screen while cooling the high-temperature light source. Also, the first lens array 54 and the second lens array 56 configured as an optical integrator can irradiate a uniform illumination light on the liquid crystal panels 63, 69, 76, thus producing a bright, large image on the screen with a uniform peripheral illuminance. In the conventional liquid crystal projector of this configuration, however, has the problem that the hot air 84 exhausted by the exhaust fan 83 often flows toward the viewers located in the neighborhood of the liquid crystal projector and thus gives the feeling of discomfort to the viewers. Also, the liquid crystal projector is sometimes used in the vicinity of the video equipment such as the personal computer liable to succumb to heat easily. In such a case, such video equipment is required to be located at a position not exposed to the hot air. Further, in order to efficiently exhaust the heat generated from the light source, care must be exercised not to place any object constituting a stumbling block to the exhaustion in a path of the hot air, thereby posing the problem of operating inconveniences.
On the other hand, JP-A-5-59424 (UM) proposes a configuration in which an exhaust fan for cooling a light source is arranged in the same plane as the front cylinder section of a projection lens so that the light is projected in the same direction as the hot air is exhausted. In this configuration, the hot air exhausted from the exhaust fan is prevented from flowing toward the viewers located in the neighborhood of the liquid crystal projector. The viewers thus feel no inconvenience, nor is it necessary to take care not to arrange the equipment easily affected by heat in the neighborhood of the liquid crystal projector or to place an object constituting a stumbling block to the exhaustion in a path of the hot air. It is thus possible to obtain a liquid crystal projector convenient to use. Nevertheless, this configuration fails to take into consideration the fact that the hot air exhausted from the exhaust fan may flow into the projected light from the projection lens and cause fluctuations of the image projected on the screen. Also, no care is taken about a configuration of wind-directing plates to assure an efficient exhaustion of the hot air. Further, no special consideration is taken about the configuration of the optical system including the first lens array and the second lens array.
Furthermore, in the conventional liquid crystal projector having the above-mentioned configuration, the reflector 52 is a parabolic mirror and therefore parallel light rays enter the first lens array 54, thereby leading to the disadvantage that the first lens array 54, the cold mirror 55, the second lens array 56 and the dichroic mirror 57 increase in size. The increased size of the second lens array 56 results in another disadvantage that the light utilization rate of a liquid crystal panel with micro-lenses, if employed, cannot be improved. The reason why the use of a liquid crystal panel with micro-lenses deteriorates the light utilization rate will be described with reference to FIGS. 10, 11, 12. FIG. 10 is a sectional view of a liquid crystal panel 85 with micro-lenses. Even when completely parallel light rays 86 are assumed to enter the liquid crystal panel 85, these light rays 86 emit from the liquid crystal panel as divergent light rays 88 at an angle e under the effect of the micro-lenses 87. Since the divergent light rays 88 pass through a pixel aperture 90 without being interrupted by a black matrix 89, however, the effective vignetting factor of the liquid crystal panel is improved for a higher light utilization rate. FIG. 11 is a diagram showing light rays from the second lens array 56 to a projection lens aperture 92 designed for a liquid crystal panel 91 without any micro-lenses. The incident angle f and the outgoing angle g of the liquid crystal panel 91 are designed to be equal to each other. FIG. 12 is a diagram showing light rays from the second lens array 56 to the projection lens aperture 92 for a liquid crystal panel 85 with micro-lenses. As apparent in comparison with FIG. 11, the liquid crystal panel with micro-lenses as shown in FIG. 12 has the outgoing angle g of the liquid crystal panel 85 increased by an amount equivalent to the divergent angle e. Even when the effective vignetting factor is improved by the micro-lenses 87, therefore, the eclipse developed at the projection lens aperture 92 prevents the light utilization rate from being improved.